Spin-on filters are commonly used to separate contaminants from fluid. Spin-on filters typically mount on a mounting adaptor of a fluid circuit and receive and return fluid therefrom. Spin-on filters typically include a steel canister housing a filter element, having a closed end and an open end. At the open end, the filter has provided a connection to the mounting adaptor. The connection requires a flow path for contaminated fluid into the canister and a flow path for filtered fluid out of the canister. Threaded baseplates have commonly been used for the connection.
It is known that many lower pressure and a number of higher pressure applications exist which can be satisfied by spin-on type filters. Lower strength filters are used for lower pressure applications, pressures less than 100 p.s.i., for example in a lubrication circuit for an automobile. Current applications in hydraulics frequently use pressure differential between the high strength filters. These high strength filters are used in the hydraulic circuits of heavy machinery for use in industries such as agriculture or construction, for example, a hydraulic circuit for a backhoe which powers the shovel motion. In such hydraulic circuit applications, the filter must withstand the high pressure inside the filter and the ambient pressure outside the filter. Such applications may require that the filter be capable of withstanding pressure spikes in excess of 750 p.s.i. and impulse strength of at least 0-300 p.s.i. for sustained periods without leakage or failure.
Because of the high pressure requirements, it is preferable to have high tensile strength in the baseplate. It is also desirable to provide a baseplate that is of low cost to manufacture and assemble into the filter. Stamped steel has commonly been used for baseplates. However, aluminum die cast baseplates have provided better strength and currently cost less to manufacture. It is therefore desirable to incorporate an aluminum baseplate into the filter. However, as will be discussed, aluminum baseplate type filters have had manufacturing, assembly and cost disadvantages with providing an adequate connection to the mounting adaptor of a hydraulic circuit.
Insofar as reliability and user convenience are concerned, an important element in spin-on filters is an outer gasket which will remain in position on the filter until locked in sealing relationship with the mounting adaptor of a hydraulic circuit. Outer gaskets prevent fluid leakage between the mounting adaptor and the filter. Often, the outer gasket is installed in and preferably secured in an outer groove on the filter. It is particularly desirable to secure the outer gasket in the groove so that it does not fall out during transport or installation. To retain the outer gasket, at least one of the groove's walls typically includes a reverse draft and/or a mechanism to pinch the outer gasket in the groove.
Also common to spin-on type filters is that the baseplates have been fastened to the canister. Burst strength requirements for a filter necessitates a seaming lid fastening technique which provides a connection capable of withstanding the pressure differential applied from fluid pressure inside of the filter to the ambient outside. The fastening technique also requires torque transfer. Torque transfer has been necessary in spin-on filters because the threaded connection is commonly in the baseplate. When the canister is screwed on or off the adaptor, torque is transferred from the steel canister to the baseplate. Various methods and mechanisms have been employed to fasten the baseplates to the steel canister.
A common way of fastening the canister and baseplate has been to use a seaming lid. Seaming lids are typically stamped from sheet steel. The outer edge of the seaming lid is meshed with an edge of the canister sidewall to form a seam. Such a seaming lid and seam is shown and described in U.S. Pat. Nos. 5,490,930, to Krull, and 5,453,195, to Jorgenson et al., both assigned to the present assignee. As shown and described in Jorgenson et al. '195, the seaming lid technique has sufficiently fastened the baseplate to the canister. However, one drawback of many prior seaming lid approaches has been that the seaming lid is welded to the baseplate providing the torque transfer necessary for spin-on filters. Welding has not allowed for aluminum baseplates. Moreover, the step of welding can increase manufacturing costs. Another drawback of prior seaming lid fastening techniques has been that the outer gasket retaining groove which is often U-shaped has commonly been formed entirely in the seaming lid. Thus, additional forming and drawing of the sheet steel has been necessary which has decreased strength and increased costs.
Steel seaming lids have also been interlocked to stamped steel baseplates providing the necessary torque transfer. The seaming lids in these filters have provided tabs that fold through the oil inlet ports of the baseplate to provide torque transfer. However, this design undesirably has a substantially flat baseplate. The flat baseplate design has been necessary to provide a flatter, less formed structure in the seaming lid. These flat baseplates are undesirable because they do not permit the strength enhancing structural features desired for aluminum baseplate type filters for high pressure applications. Another very substantial drawback of these flat baseplate filters has been that the outer groove is formed entirely by the seaming lid. Further forming of sheet steel has been necessary to form the outer gasket retaining groove and outer gasket retaining mechanism in the seaming lid which has the cost and strength drawbacks mentioned above.
Other past designs have fastened the baseplate directly to the canister without a seaming lid as shown in U.S. Pat. Nos. 5,080,787; 4,743,374 and 4,834,885. Some of these filter designs have provided for aluminum die cast baseplates and high pressure applications. Filters without a seaming lid generally bead or wrap the a portion of the open end of a canister over a preformed shoulder in the baseplate. However, filter designs without a seaming lid have had manufacturing disadvantages and require additional tooling. Specifically, it has been difficult to provide for satisfactory burst strength while at the same time providing torque transfer between the canister and the baseplate and an outer gasket groove. Further drawing of the canister has often been necessary to provide a retaining groove and torque transfer which may reduce strength of the filter and increase manufacturing cost.
Another drawback is that additional geometry and small tolerances have often been necessary in the die cast of the aluminum baseplate to provide a retaining groove. Thus, the manufacturing of filters without a seaming lid has required additional geometry in the baseplate, additional parts and/or additional complex tooling to draw the sheet steel from the canister around the baseplate to sufficiently fasten the baseplate to the canister and provide a retaining groove.